Population size of Island loggerhead shrikes on Santa Rosa and Santa Cruz Islands

Abstract

Island loggerhead shrikes (Lanius ludovicianus anthonyi) are an endemic, genetically distinct subspecies of loggerhead shrike on California's Santa Rosa, Santa Cruz, and Santa Catalina Islands (USA). This subspecies is listed as a Species of Special Concern by the California Department of Fish and Game and has been petitioned for federal listing under the Endangered Species Act. The combination of suspected low numbers and the possibility of federal listing, prompted us to undertake a study to rigorously estimate the number of remaining individuals on Santa Rosa and Santa Cruz Islands. During the 2009 and 2010 breeding seasons, we surveyed sample units on Santa Rosa and Santa Cruz Islands using a double‐observer method with independent observers to estimate joint detection probabilities (p), where we selected units under a stratified random sampling design. We estimated shrike abundance to be 169 in 2009 (p = 0.476) and 240 in 2010 (p = 0.825) for Santa Rosa Island, and 35 in 2009 (p = 0.816) and 42 in 2010 (p = 0.710) for Santa Cruz Island. These numbers, especially for Santa Rosa Island, are higher than previously reported but nevertheless are still low. Rapid vegetation change on both islands due to recent removal of nonnative herbivores may threaten the habitat and status of this subspecies and, therefore, we suggest that intensive demographic and habitat use research be initiated immediately to obtain additional information vital for the management of this subspecies. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Genetic Divergence of an Avian Endemic on the Californian Channel Islands

“…l . mearnsi have been driven to precariously low population sizes with current estimates of less than 250 and 50 birds respectively [ 18 ].…”

Reintroduction of Historically Extirpated Taxa on the California Channel Islands

“…Island Scrub-Jays are nest predators. Populations of predator-naïve songbirds (such as Loggerhead Shrikes [Lanius ludovicianus]; Stanley et al 2012) on Santa Rosa could be adversely affected. However, recent work demonstrates that some Channel Island passerines modify their behavior in the presence of predators, even if they lack experience with that predator (Peluc et al 2008, Sofaer et al 2013).…”